There are very few instances when I have posted a headline like the one in this blog. Hype is not a tool I use to get the attention of my audience unless it is warranted and I feel it could help to save lives and property. What I am seeing in some of the global models is worthy of getting your attention and if it’s hype, then all the better in the long run.

There is a storm brewing in the Caribbean that will soon get a name: Sandy. Right now we know it as 99L, an area of investigation with potential to develop. Within the next 10 days, we may remember it as one of the great ocean storms of recent memory. Before all of that, it will be a problem for the Caribbean and that much is certain.

So far, development of 99L has been slow. It now looks as though things are coming together in the western Caribbean, a few hundred miles south of Jamaica. Water temps are as warm as could be and upper level winds are becoming more and more favorable. The NHC gives the area an 90% chance of becoming a tropical cyclone within 48 hours. I think it’s as good as done at this point and we’ll soon have TS Sandy to track.

72 hour ECMWF showing "Sandy" over Jamaica

People with interests in Jamaica need to be watching this system closely. It will bring periods of heavy rain and an increase in wind as it moves slowly towards the northeast with time. This slow forward motion is going to be a problem as the tropical rains will have a lot of time to fall over the same area for a couple of days or more. I would also not be surprised to see this become a hurricane before it reaches Jamaica. Intensity prediction is very poor even in this day of high-end computer models. Hopefully we’re only talking about a weak tropical storm in a few days but remember that hope is not a good planning tool. Being prepared is far better.

After Jamaica, the threat shifts to Cuba, Hispaniola and the Bahamas. Here too, the main issue will be excessive rain from what is surely to be “Sandy” by mid to late week. How strong it is depends on how quickly it can develop a solid inner core. Interests in the region should be paying close attention to what happens as this feature grows. We are not talking about an “in and out” system that gets kicked in to the Atlantic in a day or so. I think the big story will be the heavy rain even if this does become a hurricane in the Caribbean.

It’s what happens after the Caribbean that has the potential to make this storm one that people talk about for a long, long time.

Day five of the ECMWF showing "Sandy" after moving through the Bahamas

To put it in simple terms, some of the global models are indicating that this storm will get caught in the southwest Atlantic and grow in to a hybrid mix of a hurricane and a Nor’easter the likes we have not seen since as far back as 1991 with the “Perfect Storm”. The closest event I can recall is “Nor-Ida” in 2009 which took the tropical leftovers of hurricane Ida from the Gulf of Mexico and transitioned it in to an epic ocean storm that blasted the North Carolina coast and points north. I was in that one and will never forget it. This storm could make that one look like a day in the park.

It all seems to have begun yesterday when some of the global models began to change their track for 99L from an out to sea event to one that may affect people from Florida to Maine. The Canadian was one of the first to show it. Then the American based GFS and finally, the very reliable ECMWF or Euro. People began talking about it within the weather blogs as if sniffing out something that movies are made out. It was incredible to read what people were saying could happen if this came to pass. Surely it was a one time fluke in the models and things would return to normal a mere 12 hours later. Not so much.

The overnight run of the Canadian global model shows pretty much the same scenario as yesterday. It takes what would be Sandy and turns it in to this enormous ocean storm that would cause coastal flooding, high winds and heavy rains for a large portion of the U.S. East Coast.

Day 8 of the ECMWF which shows a powerful coastal storm impacting the Mid-Atlantic region

Looking at the latest Euro run, it too continues its forecast of developing a very large and powerful storm as the tropical energy from what would be Sandy gets pulled in to a deep trough digging in. This entrainment and phasing is rare but when it happens, it can lead to very powerful hybrid storms that have both tropical and non-tropical characteristics. The Perfect Storm in 1991 was just such an example. The overnight run of the Euro is jaw-dropping, there is no other way to describe it.

On the other hand, the GFS has all but abandoned this idea and simply sheds off the energy from the tropics in to a separate ocean storm way out in the open Atlantic. The result is….nothing. No big storm once 99L/Sandy leaves the Caribbean. It is remarkable to see such vast differences in the models and goes to show how complex the situation is. We are talking about an event that is forecast by some of the models to take place more than a week away. I debated whether or not I should even discuss it since it’s so far out in time. But I figured that rational people who read my blog would understand and appreciate the heads up if this in fact comes to pass….the bad storm that is. Maybe it’s all just a fantasy by the models that show it and the only concern, albeit a very legitimate one, will be for the Caribbean and the Bahamas. If not, and this storm happens the way the Euro shows it and the GFS showed it yesterday for a time, then we will be talking about this well past the hurricane season.

For now, we wait and go with the short term which is that we see what is a developing tropical depression in the western Caribbean. The first impacts will be felt in Jamaica and eastern Cuba. From there, we will just have to see how things turn out. The next several days could be very interesting if not very important in shaping how the hurricane season comes to an end.

I’ll post another short update this evening to go over the latest on the situation in the Caribbean. I’ll also have the video blog posted to our iPhone app by early this afternoon and it will incorporate the overnight model runs as well as the early morning or 12Z model runs to compare. If you don’t have our app, you’re missing out on a great tool in the daily video blog. It brings this discussion to life with numerous graphics, satellite shots and an in-depth explanation of what’s going on in the tropics now and what’s forecast several days out.

There is a lot to discuss regarding the future track and intensity of 99L as it could affect literally millions of people from the Caribbean to the U.S. East Coast.

First, the current situation. Right now, 99L is rather disorganized over the Caribbean Sea but is forecast by all of the global computer models to gradually organize and become a tropical cyclone within the next two or three days. It looks like Jamaica, eastern Cuba and Hispaniola could be in line for quite a bit of rain and wind by the middle of next week.

By Thursday, the GFS places a strengthening tropical cyclone over eastern Cuba with heavy rains spreading across the southeast Bahamas. Water temps in this region are still very warm and it is possible that we could be looking at a rather strong tropical storm by this point as most of the guidance suggests steady strengthening.

By late next week, most of the reliable model output suggests a track in to the northern Bahamas, not too far off the Florida east coast. This is important because there is likely to be an indirect impact to Florida because of the presence of this system and a high pressure area to its north. It appears that a fairly strong surface high will move off the Northeast coast late next week and it could do two things. First, the high pressure north, coupled with the deepening low pressure off of Florida, will create quite a strong pressure gradient. This means the winds will be quite stiff out of the northeast for a good deal of the east side of Florida. So at the very least, rough surf and rip currents are a good bet towards the end of the week for Florida.

The other issue is that this high could act to block what would presumably be “Sandy” from turning out to sea. In fact, both the GFS and the ECMWF show this scenario and take what looks strong enough to be a hurricane right in to the East Coast of the U.S. somewhere north of Cape Hatteras. Sea surface temperatures in this region are running a couple of degrees above normal for this time of year and have not been disturbed by a previous hurricane earlier in the season. We are going to have to watch the evolution of this pattern very carefully over the next few days. What looked like a sure bet to send “Sandy” out to sea is no longer such a home run, so to speak. This could mean that people from the Caribbean Sea to Florida and eventually the East Coast have to deal with some degree of a tropical system over the next week or so. Interests in Jamaica, Cuba, Hispaniola and the Bahamas need to watch this system closely. We’ll see how things progress and can focus more on potential U.S. impacts as we get in to next week. For now, it looks like a slow process for 99L to develop but once it does, there is potential for it to impact a lot of people over a wide geographic swath.

I’ll post more here about 99L tomorrow morning. I also will be posting regular video blogs to our iPhone app which is a great way to visually understand what I discuss here in the blog posts. If you don’t have the app, there is no better time to get it. We’ve recently added our own tracking maps and of course have the exclusive in-field weather data, live web cams and video blogs should a landfall take place.

A look at invest area 99L indicates that it is getting somewhat better organized today. A general increase in shower and thunderstorm activity can be seen in satellite imagery although it is still rather poorly organized.

For the most part, the global models are not very bullish on 99L developing much in the coming days. The GFS suggests some strengthening and it is possible that this system becomes a tropical storm as it moves towards progressively warmer water. There is still some dry air around, enough so to limit the deep convection needed to allow 99L to thrive and grow at a rapid pace.

The NHC’s intensity model, SHIPS, shows modest intensification but keeps 99L below hurricane intensity. Yesterday, that same model suggested that it would in fact become a hurricane.

The ECMWF model or Euro, shows very little in the way of strengthening as the system moves towards the Lesser Antilles.

The bottom line here is that it appears some slow development is possible as 99L tracks generally westward towards the Windward Islands. Interests there should be ready for at least an increase in shower and thunderstorm activity in the coming days. I would not be surprised to see 99L become a tropical storm but it would probably be fairly weak and not very organized. Once it moves in to the Caribbean Sea, conditions are generally not very favorable for continued development.

Elsewhere, another tropical wave is moving through the Greater Antilles islands today and will spread showers and thunderstorms across Puerto Rico, Hispaniola and eventually Cuba. None of the reliable computer models indicate that this wave will develop in the coming days. Keep in mind that tropical waves often bring periods of gusty winds and squally weather. Conditions will improve across the region by tomorrow as the wave passes on by.

Speaking of tomorrow, our app, HurricaneTrack, hits the App Store. I will have a full blog post about it and the special limited time price that we will be offering as we officially roll out version 1.0. The app will feature a daily video blog plus live weather data during hurricane and tropical storm landfalls. This version will be just the start as we plan to add more features- but that will depend on YOU to help make it a success. We will have an Android version available just as soon as possible so no worries for our Android device users, we’ve got you covered too!

The NHC is monitoring an area of low pressure well to the south and west of the Cape Verde Islands for possible development. It appears that conditions across the region are becoming more conducive for tropical cyclone formation. The dry, dusty air seen in recent weeks has significantly decreased and water temps are just warm enough to support development.

Vertical wind shear in the tropical Atlantic

Looking at some of the parameters typically associated with tropical cyclone formation, we see that vertical wind shear, the difference in wind speed and direction with height in the atmosphere, is right where it should be for this time of year. In other words, shear is not a factor. It is running at about the climatological average. This should allow for a steady growth in deep tropical thunderstorms or convection. In turn, this will allow the pressures to continue to fall as the fairly large envelope of energy gradually consolidates as it moves westward.

Vertical instability in the tropical Atlantic

On the other hand, vertical instability, which is more or less a way of saying how stable is the atmosphere. Yet another way to put it is how difficult is it to lift the air and get the vertical motion needed to create tropical convection? Right now, vertical instability is running quite a bit below the average for the tropical Atlantic. This means that we will not see rapid development of 99L. However, this is not necessarily good news. The reason? Typically, the sooner a system develops, the more chance it has to be picked up by a weakness in the subtropical ridge and track out to sea. The later the development takes place, the farther west we usually see storms and hurricanes track. So even though vertical instability is running below normal right now, it likely only means a delay in development and should not be enough to limit it completely.

Looking at the global computer models, the GFS seems to be the most consistent with development and an eventual track through the Windward Islands. The ECMWF has basically no development from this system while the Canadian CMC model seems a little too aggressive and thus has a more northerly track over the next five to six days. It during these early stages of what is called cyclogenesis that the models will waver and not be of much use. The good news is that 99L is way out in the tropical Atlantic and we will have several days to monitor its progress.

I do think that it is a good reminder that we are entering the busy months of the hurricane season. Whether or not 99L develops, August is fast approaching and the need to be ready for what the next 90 days or so brings is critical. For the next few days, folks in the Lesser Antilles should be watching 99L closely. It has a chance to develop and at least bring inclement weather to the region. How much it develops remains to be seen. It is very early in the process and much will change over the week ahead. I’ll post regular updates here and on our Facebook and Twitter pages. Keep in mind that beginning Wednesday, August 1, you will be able to purchase our brand new HurricaneTrack app for iPhone/iPod Touch (it will work on an iPad though it is not formatted for that device per se). The app will feature an in-depth daily video blog that will keep you informed through the use of graphics and narration concerning any goings on in the tropics. I’ll have a special link and blog post on Wednesday once the app is available.